irrigation – does variability matter? ian mcindoe fraser scales
DESCRIPTION
Irrigation – Does Variability Matter? Ian McIndoe Fraser Scales. Background. With irrigation, we have to get SMARTer ! Production Drainage (due to irrigation AND rainfall) Allocation limits/ water use Other factors, e.g. energy We need irrigation to be well-designed and well-managed - PowerPoint PPT PresentationTRANSCRIPT
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Irrigation – Does Variability Matter?
Ian McIndoeFraser Scales
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Background
• With irrigation, we have to get SMARTer!– Production– Drainage (due to irrigation AND rainfall)– Allocation limits/ water use– Other factors, e.g. energy
• We need irrigation to be well-designed and well-managed
• Design sets the platform for high performance
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The challenge
• We live in an imperfect world• Variability is a fact of life• Variability has to be accommodated in both
design and management• Optimum solutions are site specific
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What variability?
• Climatic – rainfall, wind, humidity, temperature
• Agronomic – crop, stage, physical composition, actual water use
• Soils – PAW, infiltration, depth to pans, surface storage
• Topographical – shape, slope, infrastructure, natural features
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What variability?
• Water supply – reliability, quantity, quality• Irrigation system – components, pressure,
flow, uniformity, application intensity• Management – timing, depth applied
• Given this, how can we deal with variability to deliver SMART irrigation?
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Climate
• Generally, good historical data is available – useful for determining design specs and overall need
• For rainfall, need to make full use of local data
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Wind speed
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Wind speed
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Temperature
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Agronomic
• Currently, mostly standard values used to determine crop water need
• Improved data is being produced – e.g. grazed pasture crop factors
• Need for irrigation systems to be designed to better match crop needs
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Soils • Currently, soil maps often used (e.g. S Map)• Need better information on soil properties
and variability of soils on farm– PAW and its variability– Depth to pans/ lower hydraulic conductivity
horizons
• How much does PAW variability matter?
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Soil PAW variability
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Soil PAW variability
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Topography
• Slope matters more than you might think• Very few paddocks are actually flat• Surface redistribution is very common• Need to tailor design and management to
maximise benefits
• Land levelling under spray irrigation?
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Application uniformity
• Is about how evenly water is being applied to the ground surface
• Easily checked using bucket tests• Low uniformity usually leads to low
efficiency
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Spray irrigation bucket test
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Application uniformity
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Application uniformity
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Ponding and surface redistribution
• Probably the biggest contributor to low irrigation performance
• Can generally be observed• Driven by application intensity and depth
applied• Particularly an issue on slopes• Needs full consideration in irrigation design
and management.
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Ponding under pivot
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Ponding
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Application intensity
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Application intensity
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Supply reliability
• Impacts on irrigation mind set – just in case versus just in time
• Impacts on production, water use, drainage
• Need to have high reliability to achieve high performance
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Irrigation system
• Irrigation method• Pressure variability - tradeoffs• Flow variability
– issue with VRI, corner arms, multiple pumps• Voltage variability• INZ Codes of practice – design, installation
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Performance – 60 mm PAW
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Performance – 60 mm PAW
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Performance – 120 mm PAW
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Performance – 120 mm PAW
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Irrigation management strategies • Depth of water applied• Return interval• Seasonal limits• Where and how irrigation is scheduled
• A lot of work has been done and is being done in this area.
• Weather forecasting will be critical!
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Effect of scheduling location
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Conclusions • We need to become SMARTer irrigators• Variability does matter in some areas• We need to focus on production, water use
and drainage • Better engineering will be required
– in the factory: new or improved irrigation methods– in the design shop
• We need to target application uniformity• We need to target surface redistribution
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Priorities
• What is easy and cost-effective to implement?– Some things are well understood– Some things need to be better communicated to
end users– Some things require further investigation
• We can achieve our targets, but its not going to be easy.
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Questions
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Temperature
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Centre-pivot